LTC1647-3IGN datasheet(13/20 Pages) LINER

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LTC1647-1/LTC1647-2/LTC1647-3

If a dead short occurs after a supply connection is made

(Figure 12), the sense resistor R1 and the RDS(ON) of fully

enhanced Q1 provide a low impedance path for nearly

unlimited current flow. The LTC1647 discharges the GATE

pin in a few microseconds, but during this discharge time

current on the order of 150 amperes flows from the VCC

power supply. This current spike glitches the power sup-

ply, causing VCC to dip (Figure 12a and 12b).

On recovery from overload, some supplies may over-

shoot. Other devices attached to this supply may reset or

malfunction and the overshoot may also damage some

components. An inductor (1

µH to 10µH) in series with

Q1’s source limits the short-circuit di/dt, thereby limiting

the peak current and the supply glitch (Figure 12c and

12d). Additional power supply bypass capacitance also

reduces the magnitude of the VCC glitch.

VID Power Controller

The two Hot Swap channels of the LTC1647 are ideally

suited for VID power control in portable computers.

Figure 13 shows an application using the LTC1647-2 on

the system side of the device bay interface (1394 PHY and/

or USB). The controller detects the presence of a periph-

eral in each device bay and controls the LTC1647-2. The

timing waveform illustrates the following sequence of

events: t1, rising out of undervoltage lockout with GATE 1

ramping up; t2, load current fault at R1; t3, circuit breaker

resets with R5/C3 delay; t4/t5, controller gates off/on

device supply with RC delay; t6, device enters undervolt-

age lockout.

If C6 is not connected in Figure 13, FAULT 2 and ON2 will

have similar waveforms. t7 initiates an ON sequence; t8, a

load fault is detected at R7 with FAULT 2 pulling low. If the

controller wants to stretch the interval between retries, it

can pull ON2 low at t9 ( t9 – t8 < 0.4•tRESET). At t10/t11, the

controller initiates a new power-up/down sequence.

APPLICATIO S I FOR ATIO

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